Our long term objective is to determine how membrane-type matrix metalloproteinases (MT-MMPs) regulate tumor invasion and metastasis. Although matrix metalloproteinases (MMPs) have been implicated in the progression of malignant cancer, the mechanism by which tumor cells deploy these destructive proteinases remains unresolved. MT-MMPs are a subset of MMPs with transmembrane domains capable of focusing these enzymes on plasma membrane against extracellular matrix (ECM) barriers, representing a novel paradigm on how tumor cells deploy proteolytic activity during tumor invasion and metastasis. We have recently demonstrated that MT1-MMP is regulated by endocytosis in clathrin- coated vesicles to control its proteolytic activity on cell surface. We established that its cytoplasmic domain is required for endocytosis and its removal gave rise to a gain-of-function mutant of this enzyme. This endocytosis-deficient mutant is more potent than wild type MT1-MMP in promoting invasiveness in prostate cancer cells, suggesting that the invasiveness of tumor cells can be regulated through the trafficking of MT-MMPs. Employing a chimera between MT1-MMP and MT3-MMP, we obtained the first evidence that internalized MT-MMPs can be recycled back to cell surface. In this application, we propose to integrate the studies of MT1-MMP and MT3- MMP to test the hypothesis that tumor cells modulate their invasiveness by controlling the trafficking of MT- MMPs through their cytoplasmic domains. First, we will define the trafficking of MT1-MMP and MT3-MMP from cell surface to various intracellular compartmetns and characterize the impact of growth factors and extracellular matrix on their trafficking. Secondly, we will define the role of cytoplasmic domains of MT1- MMP and MT3-MMP in mediating their trafficking/recycling and characterize their interactions with cellular components. Thirdly, we will define the regulatory role of trafficking on MT1-MMP and MT3-MMP mediated cell growth and invasion within or through 3-dimensional type I collagen matrix. Results from these approaches may yield insights on how tumor cells gain a growth and invasive advantage by regulating the trafficking of MT-MMPs and such insights may lead to the development of novel drugs for therapy and chemoprevention against cancer.